Apartment Rent Below Market Value

Shalom, I have a question and would appreciate it being considered in detail.We are currently renting an apartment in Telzstone and at the same time renting out our own apartment in Beit Shemesh. The rent we could have asked for in Beit Shemesh is about 500–700 shekels higher than what we agreed upon with our tenant—we signed for 4,650 shekels, while similar apartments typically rent for 5,000 to 5,500.The reason we agreed to this relatively low rent was due to a negative experience we once had as tenants, when a landlady tried to extract every penny from us. My husband decided we should act more compassionately. He also assumed that just as last year our landlord had taken our situation into account and didn’t raise the rent to the maximum market rate, this year he would act similarly.In reality, we are currently paying 4,750 shekels for our apartment in Telzstone, and our landlord now wants to raise it to 5,400.Our question is: In light of all the above, do we have any halachic grounds to reopen or renegotiate our signed rental agreement?I’ll note that our contract does include a clause that says if we decide to sell our apartment, we can inform the tenant, and they will be required to vacate within 60 days.My husband is a kollel student, I work in an office job, and we have a mortgage. This is not about being picky—we genuinely feel this was a case of "mekach ta'ut" (a mistaken transaction), and we are looking for some kind of halachic solution.Thank you very much.

Shalom UvRacha,

Answer from the Dayanim of the Beit Hora'ah:

The amount you agreed upon in the contract is binding upon you.

It is not possible to reopen the contract after signing.